Ten years ago two Colorado chemistry teachers unleashed a brash concept on a K-12 landscape where few questioned the age-old formula of lecture, homework, assess, repeat. It was the early days of YouTube (then two-years old), and it was getting cheap and easy to make and post videos, so the two teachers—Jon Bergmann and Aaron Sams—proposed shifting lectures to videos students would watch at home, and asking students to come to class prepared to problem solve with their peers. It became know as the flipped classroom—a modern, video-based version of a model pioneered by a handful of higher ed professors during the 1990s.